1. Field of the Invention
The present invention relates to an exposure apparatus for exposing the peripheral portion of a substrate particularly of a semiconductor wafer or the like.
2. Related Background Art
In the manufacture of a semiconductor wafer, the peripheral portion of a substrate is sometimes exposed at a predetermined width (in the order of 1 to 7 mm, for example) to light so as to prevent the resist from peeling off the peripheral portion of substrate. As disclosed in U.S. Pat. No. 5,168,304 and EP 461932A2, an exposure apparatus of this type is known which comprises an irradiating portion for emitting a bundle of exposure light onto the peripheral portion of a substrate, and means for controlling an exposure light width by moving the irradiating portion radially of the substrate as the substrate rotates so as to make the exposure light width on the peripheral portion of the substrate agree with a predetermined value.
In this exposure apparatus, the exposure light is relatively moved with said substrate around the overall substrate by following the outer periphery of the substrate. When, therefore, orientation flat (hereinafter referred to as the "OF") is provided on the substrate, the irradiating portion also follows the OF to maintain a constant exposure light width. The OF is made up of a cut portion for setting the substrate in position. In place of the OF, a notch having a depth of 1 mm or so or cutouts may be formed in the peripheral portion of the substrate. The irradiating portion also follows the notch or the cutouts. Since the notch and the cutouts are much smaller than the OF, it is less necessary for the irradiating portion to follow the notch or the cutouts. When the irradiating portion follows the notch or the cutouts, the light exposed regions of the peripheral portion of the substrate shift toward the center of the substrate, and this causes a problem that the effective area of the substrate (the area of the region which can form a pattern, for example) is reduced.
Further, when a deviation (a change of the shape of the outer periphery of a substrate) increases rapidly, the irradiating portion responses excessively to the deviation at the lost portion in the periphery of the wafer (i.e., the notch or the cutouts). Thus, hunting or the like is generated in the control system to render the control system unstable, thereby producing variations in light exposure widths.